This kind of linear bearing comprises a rail having ball channels in which balls are moved and secured to a bed or stationary element, and a slider having load ball channels cooperating with the ball channels to sandwich a multiplicity of balls and adapted to guide a table or movable body along the rail.
The slider has a function such that the load of the movable body is applied directly thereto. Under the circumstances, if the slider is deformed, the movable body is displaced relative to the base to which the rail is mounted. This presents a problem that the movable body can not be guided accurately on a straight line. The slider body to which the movable body is secured must have high rigidity.
To this end, the slider conventionally has a slider body formed from a metal block made, for example, of bearing steel. The slider body is made by first cutting a rectangular metal block to a predetermined shape, then, forming nonload ball bores and tapping bolt holes for securement of a movable body, and finally, carburizing a portion of the slider body and cutting and lapping that portion of the slider body to form load ball channels.
However, where a slider body is made from a metal block made, for example, of bearing steel, such a metal block must be machined in various ways. This production method is thus cumbersome.
It is necessary to accurately and smoothly cut the slider body at a predetermined angle to form load ball channels. However, it is difficult to accurately contact a grinder or other cutting tools when the slider body has a complicated shape. This deteriorates the accuracy of load ball channels.
There is proposed a slider body made from materials other than metal block. A thin metal plate has load ball channels and is molded, at its outer periphery, of epoxy concrete or synthetic resin (see Japanese utility model publication No. 48417/91)
According to this proposal, load ball channels can be readily and accurately formed by pressing or ball burnishing the thin metal plate. Also, the slider body can readily be machined to a complicated shape. This slider body can be more economically made than those formed by machining metal blocks.
However, the proposed slider body is less in rigidity than those made from metal blocks since it is like a metal plate with load ball channels attached to a block made of synthetic resin. The slider body is thus susceptible to deformation or breakage when substantial load is exerted from a movable body.
A slider must have a mounting portion for securement of a movable body. Movable bodies have various shapes and are, therefore, secured to the slider in various ways. The mounting portion may be in the form, for example, of a flange as an extension of the slider. Under the circumstances, linear bearing manufacturers are required to provide sliders with various mounting portions to meet a user's need. Its manufacture is, however, rather cumbersome. Thus, there is a need for sliders which allow for ready securement of movable bodies in various ways and which are economical to manufacture.
Conventionally, a rail is formed by drawing a metal block to have a predetermined cross section, carburizing a portion of the metal block, and cutting or lapping that portion to form ball channels. This production method is as cumbersome as that of the slider. Another problem is that the surface of the rail where balls are moved is susceptible to cracking.
There has recently been proposed a rail which includes a thin metal plate in which ball channels are formed by press, and synthetic resin inserted within the metal plate (see Japanese laid-open utility model publication No. 43521/90). However, to give ball channels predetermined hardness, it is necessary to treat the metal plate with TUFFTRIDE or thermally treat the metal plate such as quenching to harden the surfaces of the ball channels on which balls are moved. This treatment is also cumbersome and does not improve the fragility of the surfaces on which balls are moved.